1. Field of the Invention
The invention relates to a rolling bearing apparatus including a bearing portion and a lubrication unit that feeds a slight amount of lubricant to the bearing portion.
2. Description of Related Art
A rolling bearing is used, for example, as a bearing for a main spindle in a machine tool. As depicted in FIG. 5, a housing 90 included in a main spindle apparatus in a machine tool is provided with a plurality of rolling bearings 91 along an axial direction. For the main spindle apparatus depicted in FIG. 5, oil air lubrication is adopted in order to provide the rolling bearings 91 with lubricity. However, the oil-air lubrication involves high running costs due to air consumption. The oil-air lubrication also needs associated facilities such as an oil air feeding apparatus and an air clean unit, which may lead to increased facility costs.
Thus, as another means for lubricating the rolling bearings 91, a rolling bearing apparatus with a lubrication unit assembled therein as disclosed in, for example, Japanese Patent Application Publication No. 2004-108388 (JP 2004-108388 A) is known. In this bearing apparatus, a lubrication unit is installed at an inner peripheral side of outer rings of the rolling bearings and integrated with the rolling bearings (bearing portions). The lubrication unit includes a tank in which a lubricant is retained and a pump that discharges the lubricant in the tank into an annular space between inner rings and the outer rings,
An example of a pump used for the above-described bearing apparatus is depicted in FIG. 6. A pump 90 has a main body portion 91, a piezoelectric element 93, and a diaphragm 94. The main body portion 91 has an internal space 92 in which a lubricant is retained, and is open at one end of the main body portion 91. The piezoelectric element 93 is fixed to the diaphragm 94. The diaphragm 94 is fixed to a part of the main body portion 91 so as to close the opening of the main body portion 91. The piezoelectric element 93 operates to deform the diaphragm 94, thereby the volume of the internal space 92 is changed and thus the lubricant can be discharged through a nozzle 95.
As depicted in FIG. 6, a channel 97 or the like connected to the nozzle 95 is formed in the main body portion 91. The shape of the pump is complicated, and thus, the main body portion 91 is preferably formed of resin and produced by injection molding. In contrast, the diaphragm 94 is formed of a thin metal member. The main body portion 91 and the diaphragm 94 are formed of the different materials as described above, and are thus fixed together with an adhesive 96.
However, in this case, the diaphragm 94 is elastically deformed while being driven by the piezoelectric element 93. Thus, when the pump has been in use over the long term, the adhesive strength of the adhesive 96 decreases. As a result, the diaphragm 94 may be peeled off from the main body portion 91. In particular, when oil or moisture in the environment adheres to the adhesive 96, the adhesive strength may further decrease. When the diaphragm 94 is peeled off, the lubricant may leak out through the peel-off portion. Consequently, the lubricant may be inappropriately discharged.